A depth of cut adjustment mechanism is an integral part of virtually every router. Most portable routers consist of two pieces, the first consisting of a base portion having a vertical cylindrical shaft, and the second comprising a motor portion which is adjustably positioned within the shaft. The depth of cut of the blade is adjusted by mechanically adjusting the position of the motor in the base.
Examples of mechanical depth adjustment for a router are found in Moretti et al, U.S. Pat. No. 2,867,251 and Hawley et al, U.S. Pat. No. 3,443,479. Each of these patents disclose routers having vertically threaded housings on the motors which engage threads on the inside of the shaft of the base. Depth adjustment is made simply by rotating the motor relative to the base. These adjustment mechanisms are useful but do not allow a continuous adjustment of the depth of the router blade during cutting. In other words, any time the operator desires to change the depth of cut he must turn the router off, adjust the depth by turning the threads, lock the adjustment in place, and turn the router back on.
It is also known to have a router which has a motor biased relative to a base. Williams, U.S. Pat. No. 3,332,462, shows a spring-mounted attachment for use in template routing. This attachment fixes to the bottom of the router base and consists of a spring-mounted piston having a guide collar concentric with the router bit. In the normal position, the collar surrounds the bit preventing contact of the bit with the template. When the collar is placed in the opening in the template the weight of the router compresses the spring, extending the bit through the collar and into the work piece. The collar remains in the template and protects the template during use of the router.
A router having a spring-biased telescoping base unit is disclosed in Ambler, U.S. Pat. No. 3,791,260. A helical compression spring mounted in the base encircles the motor and retains it in a retracted position for plunge cutting. The depth of cut may be preset while the router is in the retracted position and the router than placed over the work piece. The router motor is then turned on and the motor is then pressed downwardly against the bias of the spring until it engages the preset locking device which locks the motor into operating position. When the cutting operation is finished, the lock is released and the router will return to retracted position. As with all other routers, only a single cutting depth is envisioned for each operation.
In recent years many operators have developed an advanced degree of sophistication in the use of the router which enables the router to be used to create very artistic work pieces. A skilled operator can turn out very attractive free hand signs containing script-type lettering in a matter of just a few minutes. In addition, routers are finding increasing use among hobbists who enjoy designing artistic woodworking pieces. A serious limitation on the use of the router is the necessity for stopping the router, unlocking the depth adjustment mechanism, and resetting it anytime the operator desires to cut at a different depth. No provision has been made for a portable router which will enable the operator to vary the depth of cut while the router is in use.
Accordingly, it is an object of the invention to provide an attachment for a portable router which will enable continuous depth-of-cut adjustment. It is another object of the invention to provide a simple, continuous depth of cut adjustment mechanism which can be quickly and easily placed on a conventional router. It is yet a further object of the invention to provide an inexpensive, easily manufactured device which can be slipped over a conventional router motor housing without the use of special tools.